The skeletal anatomy of Manchurochelys manchoukuoensis (Pan-Cryptodira: Sinemydidae) from the Lower Cretaceous Yixian Formation

ABSTRACT

Manchurochelys manchoukuoensis is a sinemydid stem-cryptodire turtle known by fossils from the Lower Cretaceous beds exposed in western Liaoning and Inner Mongolia of China. This fossil taxon is important for understanding the origin and evolution of Cryptodira (crown-group hidden-neck turtles). The holotype of M. manchoukuoensis was presumably lost during the Second World War and several aspects of the osteology of the species remains unknown. We here describe a near-complete fossil skeleton coming from the Lower Cretaceous Yixian Formation, western Liaoning, China, 50 km away from the type locality in the same formation. PKUP V1071 represents the most completely preserved specimen of the species and includes a well-preserved plastron, which was otherwise only known partially in the lost holotype. We provide a detailed osteological description of M. manchoukuoensis including data from micro-CT and X-ray computed laminography scanning of PKUP V1071. Of particular significance is the anchor-shaped entoplastron transversely extending to completely separate the small and triangular epiplastra from the hyoplastra; this peculiar morphology is otherwise only present in Sinemys spp. among turtles. Additional novel insights into plastron and cranial anatomy further support a close relationship between Sinemys and Manchurochelys.

KEYWORDS:

• Manchurochelys manchoukuoensis
• Sinemys
• Sinemydidae
• Cryptodira
• X-ray computed laminography
• Jehol Biota

Acknowledgments

We thank Walter Joyce and Donald Brinkman for carefully reviewing the manuscript. This research was funded by grants from the National Natural Science Foundation of China (NSFC 41672003), and Taishan Scholar Program of Shandong Province (grant no. 247 tsqn201812070). We thank F. F. Yin (Institute of Vertebrate Paleontology and Paleoanthropology, China Academy of Science, Beijing, China) for assistance on X-ray computed laminography scanning of the specimen and Q. F. Fang (China University of Geosciences, Beijing, China) for help with µCT scanning of the skull. M.R. was supported by the Volkswagen Stiftung “Research in Museums grant” (Az. 90 978). Walter Joyce, Donald Brinkman, Igor Danilov, and Haiyan Tong are thanked for useful discussions.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [NSFC 41672003]; Volkswagen Stiftung ‘Research in Museums grant’ [Az. 90 978]; Program for Innovative Research Team of Excellent Talents in University of Shandong Province [2019KJH004]; Taishan Scholar Program of Shandong Province [tsqn201812070].